The program lnusertemp (not Inusertemp) is run every time you start KDE. It creates three symbolic links in your .kde4 directory if they don't exist:
~/.kde4/socket-localhost.localdomain pointing to ~/tmp/ksocket-<yourname>
~/.kde4/tmp-localhost.localdomain pointing to ~/tmp/kde-<yourname>
~/.kde4/cache-localhost.localdomain pointing to /var/tmp/kdecache-<yourname>
"~" stands for "/home/<yourname>", and in some setups "localhost.localdomain" might be just "localhost".
The most likely reason for your error message is that either your ~/tmp or your /tmp directory really is full, which could mean that you are running out of space in /home or in your root directory. Try emptying both /tmp and ~/tmp. That may not be enough though: you may have to remove a number of larger files too.
But the reason for the error message could also be that there is something wrong with your existing links or their targets.
So if emptying your tmp directories and freeing up some space in /home or / doesn't help, remove the three links (~/.kde4/socket-localhost.localdomain, ~/.kde4/tmp-localhost.localdomain and ~/.kde4/cache-localhost.localdomain) - and log out. They will be recreated when you log in again.
But the first thing you should do is the first thing Phil told you to do. Type df in a terminal. That will tell you whether your partitions are full or not.
